1. Field of the Invention
The present invention relates to a frame synchronization device which uses a symbol for synchronization in which a known data series is repeatedly arranged to perform synchronization processing of a received frame, a communication terminal apparatus in which the device is used and a frame synchronization method.
2. Description of the Related Art
To perform communication, mutual synchronization needs to be secured between transmission and reception sides. A method for establishing the synchronization differs with a method or protocol of communication. Here, an orthogonal frequency division multiplexing (OFDM) method will be described.
In the OFDM method, the symbol for synchronization in which arrangement of a known data series is repeated a plurality of times is used to establish the synchronization of a frame among communication apparatuses. This symbol for synchronization is disposed immediately before a data frame, and generally called a preamble. A reception apparatus of the OFDM method in which this preamble is used to establish the synchronization is disclosed, for example, in Jpn. Pat. Appln. KOKAI Publication No. 2000-349733.
In the frame synchronization device of the reception apparatus disclosed in this document, first a rising edge is detected from a received signal to find the top of a section of the symbol for synchronization (preamble). This section of the symbol for synchronization is divided for each known data series. A correlated value of each divided data series with the known data series held beforehand is calculated. The calculated correlated values for the symbols for synchronization are added, and timing when the added result indicates a peak value is detected. This timing is assumed as a synchronization timing that indicates the top of the data frame, and a processing section of fast Fourier Transform (FFT) is set based on the synchronization timing.
The above-described frame synchronization device has the following problems.
First, when noises are mixed, the peak value after addition is sometimes generated at an unexpected timing. Moreover, when an influence of fluctuation of reception intensity is exerted, a rising edge is not normally detected. The number of symbols of the preamble that can be used in frame synchronization sometimes fluctuates. In this manner, detection precision of the synchronization timing is sometimes deteriorated and incorrect synchronization occurs in accordance with a reception situation.
An object of the present invention is to provide a frame synchronization device which can correctly establish frame synchronization, a communication terminal apparatus which uses the device and a frame synchronization method.